1. Field of the Invention
The present invention relates to a load measuring apparatus for vehicles. More particularly, the present invention relates to a vehicle load measuring apparatus which measures an amount of a load based on the distortion of an axle caused by the load that is applied to the vehicle and transmitted to the axle through a transmission member.
The present application is based on Japanese Patent Application Nos. 2000-077247 and 2000-113476, which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, a load of a vehicle has been measured mainly as for a large-sized vehicle such as trucks. When an excessive amount of goods is loaded on a truck etc., the driving operability of the vehicle is degraded, which may not only cause a traffic accident but also damage the vehicle or the surface of the road. The load measurement of a vehicle is performed in order to prevent such phenomena. Usually, the load measurement of a vehicle is performed by a load measuring apparatus disposed on the road in the following manner. That is, a wheel of the vehicle is placed on a loading plate having a load converter to thereby measure a wheel load or an axle load of the wheel. The wheel loads etc. of all the wheels of the vehicle are summed to obtain a vehicle weight. The weight of all the passengers and the weight of the vehicle itself are subtracted from the vehicle weight thus measured to obtain the weight of the load mounted on the vehicle.
However, since the aforesaid load measuring apparatus is large in its size and the mounting cost thereof is high, the location where the apparatus is disposed and the number of the apparatuses to be disposed are quite limited. Thus, the number of vehicles subjected to the measurement of loads mounted thereon is only a part of the entire vehicles, so that it is insufficient to prevent the excessive loading of the vehicles. Therefore, there has been proposed a load measuring apparatus for measuring a load at every vehicle wherein a load applied to the load-carrying platform of a vehicle is transmitted to the axle, and an amount of distortion of the axle caused by the load is measured to thereby measure the load of the vehicle.
FIG. 11 is an exploded perspective view of a conventional assembled portion for a vehicle including a load-carrying frame 1, an axle 2, a leaf spring (corresponding to a transmission member) 3 etc. Two supporting portions la are provided at the side wall of the load-carrying frame 1 so that the supporting portions la support the both ends of the leaf spring 3, respectively. The center portion of the leaf spring 3 is fixed to an axle casing 2a provided at the axle 2 by attachment members 6. A sensing element 7 for measuring a distortion amount of the axle 2 is fixed on the upper surface of the axle 2. The conventional load measuring apparatus is arranged to measure a distortion amount due to a load applied to the sensing element 7 to thereby measure the load at every vehicle.
However, according to the aforesaid conventional load measuring apparatus, the center of the load transmitted to the axle casing 2a through the leaf spring 3 from the load-carrying frame 1 moves due to the distortion of the load-carrying frame 1 and the friction etc. between the axle and the leaf spring 3 caused by the loading and unloading of goods and the running state etc. of a vehicle. As a result, since the bending moment of the axle 2 changes, there arises a problem that the relation between an amount of the load of the vehicle and a mount of the distortion of the axle 2 is broken and so a value of the load to be measured becomes erroneous.
In this respect, FIGS. 12A and 12B are diagrams for explaining the center of a load when the load is small and large, respectively. FIG. 13 is a diagram showing the conventional relation between an amount of a load and a distortion error of an axle. In FIG. 13, an ordinate represents a distortion error (%) of an axle and an abscissa represents an amount (ton) of a load mounted on a vehicle.
As shown in FIG. 12A, when a load applied to the load-carrying frame 1 is small, since stress generated at a tire in accordance with the load transmitted from the ground is small, the center of a load vector v transmitted to the axle casing 2a from the leaf spring 3 locates almost at the center of the axle casing 2a. In contrast, as shown in FIG. 12B, when a load applied to the load-carrying frame 1 is large, since stress generated at a tire in accordance with the load transmitted from the ground is large, flexible distortion is generated at the load-carrying frame 1, the axle 2 etc. Thus, the center of a load vector v transmitted to the axle casing 2a from the leaf spring 3 deviates from the center of the axle casing 2a. 
Therefore, as shown in FIG. 13, in accordance with the change of an amount of a load on a load-carrying platform due to a loading process A and an unloading process B, the center position of a load transmitted to the axle casing 2a from the leaf spring 3 changes, so that the relation between an amount of the load of the vehicle and an mount of the distortion of the axle 2 becomes broken. That is, there arises a hysteresis error that amounts of distortion of the axle differ between the loading process A and the unloading process B and hence the measured value of a load becomes erroneous. In this manner, the measuring accuracy of the load measuring apparatus for vehicles is degraded.
In view of the aforesaid problems of the conventional technique, an object of the present invention is to provide a load measuring apparatus for vehicles which can improve measuring accuracy of a load.
In order to attain the aforesaid object, according to a first aspect of the present invention, there is provided a vehicle load measuring apparatus, which measures an amount of distortion of an axle caused by a load that is applied on a vehicle and transmitted to the axle through a transmission member, and which measures a value of the load based on the measured amount of the distortion, the load measuring apparatus comprises a load concentration unit, which is disposed between the transmission member and the axle, and receives the load concentrically. Accordingly, since the load transmitted to the axle through the transmission member is concentrically received by the load concentration unit, even if there occurs the distortion of the load-carrying frame and the friction etc. between the axle and the transmission member caused by the loading and unloading of goods and the running state etc. of the vehicle, the moving range of the center of the load transmitted to the axle can be made small. Accordingly, the hysteresis error caused in accordance with the relation between amounts of a load mounted on the vehicle and amounts of the distortion of the axle can be reduced, so that the measurement accuracy of loads measured based on the distortion amounts of the axle can be improved.
According to a second aspect of the present invention, it is preferable that a contact surface of the load concentration unit, which contacts with the axle, has a shape that restricts movement of the load transmitted to the axle. According to the load measuring apparatus as in the second aspect of the present invention, the load applied to the vehicle is transmitted to the transmission member and the load thus transmitted is transmitted to the axle in a manner that movement of center of the load is restricted by the load concentration unit. Thus, since the axle receives a load from the edge of the load concentration unit, the moving range of the center of the load transmitted to the axle can be restricted within the contact surface of the load concentration unit to the axle. For example, the moving range of the center of a load of a vehicle with a large moving range can be made small by employing the load concentration unit having the contact surface area smaller than the moving range of the center of a load of this vehicle. Accordingly, the hysteresis error caused in accordance with the relation between amounts of a load mounted on the vehicle and amounts of the distortion of the axle can be reduced, so that the measurement accuracy of loads measured based on the distortion amounts of the axle can be improved.
According to a third aspect of the present invention, it is preferable that, in the load measuring apparatus as in the first or second aspect, an area of a contact surface of the load concentration unit, which contacts with the axle, is set to a value to deviate from plastic deformation range of the load concentration unit and to be minimized. According to the load measuring apparatus as in the third aspect of the present invention, the axle is provided with the load concentration unit which is arranged so that the contacting area thereof to the axle is set to deviate from the plastic deformation range of the load concentration unit and be small. The load concentrically received by the load concentration unit is transmitted to the axle. Thus, the smaller the contacting area between the load concentration unit and the axle is, the smaller the hysteresis error caused in accordance with the relation between amounts of a load mounted on the vehicle and amounts of the distortion of the axle becomes. However, when the load concentration unit is made too small, the load concentration unit is deformed by a load applied thereto. Therefore, the load concentration unit can be minimized by setting the contacting area between the load concentration unit and the axle so as to deviate from the plastic deformation range of the load concentration unit and be small. Accordingly, since the load can be transmitted to the axle more concentrically by the load concentration unit, the hysteresis error caused in accordance with the relation between amounts of a load mounted on the vehicle and amounts of the distortion of the axle can be reduced, so that the measurement accuracy of loads measured based on the distortion amounts of the axle can be improved.
According to a fourth aspect of the present invention, it is preferable that, in the load measuring apparatus as in the first, second or third aspect, the load concentration unit has a shape that prevents the transmission member from directly contacting with the axle at a time of mounting a load of maximum loading capacity of the vehicle. According to the load measuring apparatus as in the fourth aspect of the present invention, the axle is provided with the load concentration unit which is formed to have the shape that prevents the transmission member from directly contacting with the axle at a time of mounting the load of maximum loading capacity of the vehicle. Further, only the load concentrically received by the load concentration unit is transmitted to the axle. The load concentration unit suitable for the vehicle can be formed by determining, for example, both the areas of the contact surfaces thereof to the axle and the transmission member and the distance between both contact surfaces of the load concentration unit, that is, the thickness of the load concentration unit, by taking the distortion of the transmission member at the time of mounting a load of the maximum loading capacity into consideration. Thus, the load concentration unit having the shape accorded to the kind and type of the vehicle is provided between the transmission member and the axle to thereby prevent the transmission member from directly contacting to the axle even at the time of mounting a load of the maximum loading capacity of the vehicle, so that the accurate load can be transmitted to the axle through the load concentration unit. Accordingly, when the load concentration unit is formed so as to accord to the kind and type of the vehicle having a different maximum loading capacity, the load measuring apparatus for vehicles capable of measuring a load with a high accuracy can be provided easily at every type of vehicle.
According to a fifth aspect of the present invention, it is preferable that, in the load measuring apparatus as in the first, second, third or fourth aspect, the load concentration unit is formed separately from the axle. According to the load measuring apparatus as in the fifth aspect of the present invention, the load concentration unit formed separately from the axle is attached to the axle and a load concentrically received by the load concentration unit is transmitted to the axle. Thus, since it is possible to form the load concentration unit separately from the axle, the load concentration unit can be formed by material different from that of the axle. For example, it is possible to employ material with a small plastic deformation range for the load concentration unit. Further, the load concentration unit may be realized by a known member such as a height adjusting member used for a different object. In this manner, since the load concentration unit can be formed with the general-purpose properties, the load concentration unit can be formed easily in accordance with various types of vehicles. Accordingly, the load measuring apparatus for vehicles capable of measuring a load with a high accuracy can be provided easily at every type of vehicle.
According to a sixth aspect of the present invention, it is preferable that the load measuring apparatus as in the first, second, third, fourth or fifth aspect further comprises a distortion sensor disposed on the axle, wherein the load concentration unit is provided at a position where hysteresis error of an amount of distortion of the axle detected by the distortion sensor is reduced. According to the load measuring apparatus as in the sixth aspect of the present invention, the load concentration unit is provided at the position where hysteresis error of an amount of distortion of the axle detected by the distortion sensor provided at the axle is reduced. Only a load concentrically received by the load concentration unit is transmitted to the axle. In this manner, in order to reduce the hysteresis amount detected by the distortion sensor of the axle, for example, the optimum position of the load concentration unit is investigated through experimentation or simulation and the load concentration unit is provided at the position determined in accordance with the result of the experimentation or simulation. Thus, since twisting phenomenon etc. is prevented from occurring at the axle, the distortion sensor can accurately measure a distortion amount according to a load transmitted to the axle through the load concentration unit. Accordingly, when the load concentration unit is provided at the optimum position accorded to the kind and type of the vehicle, the load measuring apparatus for vehicles capable of measuring a load with a high accuracy can be provided easily.